The following applications are hereby incorporated herein by reference in their entirety and made part of the present application:
1) U.S. Provisional Application Ser. No. 60/097,569, entitled xe2x80x9cAdaptive Rate Speech Codecxe2x80x9d filed Aug. 24, 1998;
2) U.S. patent application Ser. No. 09/154,675, entitled xe2x80x9cSpeech Encoder Using Continuous Warping In Long Term Preprocessing,xe2x80x9d filed Sep. 18, 1998;
3) U.S. patent application Ser. No. 09/156,814, entitled xe2x80x9cCompleted Fixed Codebook For Speech Encoder,xe2x80x9d filed Sep. 18, 1998;
4) U.S. patent application Ser. No. 09/156,649, entitled xe2x80x9cComb Codebook Structure,xe2x80x9d filed Sep. 18, 1998;
5) U.S. patent application Ser. No. 09/156,648, entitled xe2x80x9cLow Complexity Random Codebook Structure,xe2x80x9d filed Sep. 18, 1998;
6) U.S. patent application Ser. No. 09/156,650, entitled xe2x80x9cSpeech Encoder Using Gain Normalization That Combines Open And Closed Loop Gains,xe2x80x9d filed Sep. 18, 1998;
7) U.S. patent application Ser. No. 09/156,832, entitled xe2x80x9cSpeech Encoder Using Voice Activity Detection In Coding Noise,xe2x80x9d filed Sep. 18, 1998;
8) U.S. patent application Ser. No. 09/154,654, entitled xe2x80x9cPitch Determination Using Speech Classification And Prior Pitch Estimation,xe2x80x9d filed Sep. 18, 1998;
9) U.S. patent application Ser. No. 09/154,657, entitled xe2x80x9cSpeech Encoder Using A Classifier For Smoothing Noise Coding,xe2x80x9d filed Sep. 18, 1998;
10) U.S. patent application Ser. No. 09/156,826, entitled xe2x80x9cAdaptive Tilt Compensation For Synthesized Speech Residual,xe2x80x9d filed Sep. 18, 1998;
11) U.S. patent application Ser. No. 09/154,653, entitled xe2x80x9cSynchronized Encoder-Decoder Frame Concealment Using Speech Coding Parameters,xe2x80x9d filed Sep. 18, 1998;
12) U.S. patent application Ser. No. 09/154,663, entitled xe2x80x9cAdaptive Gain Reduction To Produce Fixed Codebook Target Signal,xe2x80x9d filed Sep. 18, 1998;
13) U.S. patent application Ser. No. 09/154,660, entitled xe2x80x9cSpeech Encoder Adaptively Applying Pitch Long-Term Prediction and Pitch Preprocessing With Continuous Warping,xe2x80x9d filed Sep. 18, 1998.
A microfiche appendix B is included of a computer program listing. The total number of microfiche is 1. The total number of frames is 24.
1. Technical Field
The present invention relates generally to speech encoding and decoding in voice communication systems; and, more particularly, it relates to various techniques used with code-excited linear prediction coding to obtain high quality speech reproduction through a limited bit rate communication channel.
2. Related Art
Signal modeling and parameter estimation play significant roles in communicating voice information with limited bandwidth constraints. To model basic speech sounds, speech signals are sampled as a discrete waveform to be digitally processed. In one type of signal coding technique called LPC (linear predictive coding), the signal value at any particular time index is modeled as a linear function of previous values. A subsequent signal is thus linearly predictable according to an earlier value. As a result, efficient signal representations can be determined by estimating and applying certain prediction parameters to represent the signal.
Applying LPC techniques, a conventional source encoder operates on speech signals to extract modeling and parameter information for communication to a conventional source decoder via a communication channel. Once received, the decoder attempts to reconstruct a counterpart signal for playback that sounds to a human ear like the original speech.
A certain amount of communication channel bandwidth is required to communicate the modeling and parameter information to the decoder. In embodiments, for example where the channel bandwidth is shared and real-time reconstruction is necessary, a reduction in the required bandwidth proves beneficial. However, using conventional modeling techniques, the quality requirements in the reproduced speech limit the reduction of such bandwidth below certain levels.
Further limitations and disadvantages of conventional systems will become apparent to one of skill in the art after reviewing the remainder of the present application with reference to the drawings.
Various aspects of the present invention can be found in an embodiment of a speech encoder using an analysis by synthesis approach on a speech signal. The speech encoder comprises an adaptive codebook, a plurality of subcodebooks, and an encoder processing circuit. The encoder processing circuit utilizes parameters of the speech signal in favoring at least one of the plurality of subcodebooks over at least one other of the plurality of subcodebooks. Of course many variations are possible. For example, the speech signal may comprise a residual signal, and at least one of the parameters utilized may comprise pitch correlation, average to peak ratio, signal to noise ratio, etc. Similarly, the encoder processing circuit may also utilize a classifier in favoring the at least one of the plurality of subcodebooks over the at least one other of the plurality of subcodebooks.
Further aspects may be found in a similar speech encoder that also uses an analysis by synthesis approach on a speech signal. The speech encoder comprises a noise-like codebook, a pulse codebook, and an encoder processing circuit. The encoder processing circuit identifies a weighting to favor one of the noise-like codebook and the pulse codebook over one other of the noise-like codebook and the pulse codebook.
The identification of the weighting by the encoder processing circuit may involve consideration of pitch correlation, an average to peak ratio, and/or a signal to noise ratio. It may also involve application of a classifier which may, for example, identify a noise-like unvoiced residual. The identification of the weighting by the encoder processing circuit may also comprise applying a first weighting approach if a noise-like residual is detected, and a second weighting approach if the noise-like residual is not detected. The first and second weighting approaches may also both utilize a plurality of parameters extracted from the speech signal.
Other aspects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.